The present invention relates to an apparatus and method for detecting decrease in air-pressure for use in a two-wheeled vehicle as well as to a program for judging decompression for use in a two-wheeled vehicle. More particularly, it relates to an apparatus and method for detecting decrease in air-pressure for use in a two-wheeled vehicle and a program for judging decompression for use in a two-wheeled vehicle for judging a decrease in air-pressure of a tire especially designed for two-wheeled vehicles and for accordingly alarming a driver thereof.
Conventional apparatuses for alarming decrease in tire air-pressure can be roughly divided into direct detecting type apparatuses in which pressure sensors are mounted to tire valves for detecting air-pressures thereof and those of indirect methods in which decompression is judged on the basis of rotational velocity information of the wheels.
While the directed detecting type apparatuses are advantaged in that they are capable of informing absolute pressure values, they are simultaneously disadvantaged in that costs involved will be remarkably high owing to the fact that pressure sensors, transmitters and receivers are required.
On the other hand, while apparatuses of the indirect method cannot provide absolute pressure values, they are capable of exhibiting the merit of remarkably low costs involved due to which reason they are employed by many automobile manufactures. One example of such apparatuses of indirect method is disclosed in Japanese Unexamined Patent Publication No. 305011/1988. Such an apparatus is for detecting decrease in air-pressure of a tire on the basis of relative changes in wheel speeds, and judgments are performed through variations in the following judged values (DEL) which might be calculated on the basis of the wheel speeds:
DEL={(V1+V4)/2xe2x88x92(V2+V3)/2}/{(V1+V2+V3+V4)/4}xc3x97100(%)
Here, V1, V2, V3 and V4 respectively denote wheel speeds of a tire of the front left wheel, a tire of the front right wheel, a tire of the rear left wheel and a tire of the rear right wheel.
The apparatus as disclosed in the above Japanese Unexamined Patent Publication No. 305011/1988 utilizes the fact that a decrease in internal pressure of a tire results in a decrease in the dynamic load of the tire whereupon the rotational number of only the tire in question is increased to thus lead to an increase in the above judged value, and upon obtaining a difference between a sum of one group of diagonally located tires and a sum of the other group of diagonally located tires, it is possible to eliminate influences of slip rates of front and rear wheels.
While a decrease in internal pressure can be detected on the basis of variations of such judged values in the case of a four-wheeled vehicle, in the case of a two-wheeled vehicle, a decrease in internal pressure can not at all be detected by merely watching the ratio of rotational numbers of the front and rear wheels since no diagonal sums can be obtained as with four-wheeled vehicles.
This is due to the fact that the ratio of rotational numbers of the front and rear tire, that is, a slip rate is largely varied in accordance with running conditions even though no changes in the internal pressure of the tire occur. The slip rate might vary by 10% and more especially when performing acceleration or deceleration. On the other hand, even a decrease of 30% present in the internal pressure of the tire only results in an increase of the rotational number of several % so that a decrease in internal pressure cannot be detected by watching the ratio of front and rear wheels alone.
The present invention has been made in view of these facts, and it is an object thereof to provide an apparatus and a method for detecting decrease in tire air-pressure for use in a two-wheeled vehicle and a program for judging decompression for use in a two-wheeled vehicle capable of judging a decrease in air-pressure of a tire of a two-wheeled vehicle for ensuring safe driving.
In accordance with the present invention, there is provided an apparatus for detecting decrease in air-pressure for use in a two-wheeled vehicle, including: a wheel speed detecting means for detecting wheel speeds of a front and a rear wheel of a two-wheeled vehicle; an acceleration calculating means for obtaining accelerations of a vehicle body of the two-wheeled vehicle; a slip rate calculating means for calculating slip rates when the acceleration of the vehicle body is in a specified range which is proximate to zero; an average value calculating means for obtaining average values of the slip rates and average vehicle body speeds in case the accelerations of the vehicle body have continued to be in the specified range which is proximate to zero for a specified period of time; a difference calculating means for obtaining differences between the average values of the slip rates and a reference value which is based on an average vehicle body speed as preliminarily set when an internal pressure is normal; and a means for judging decrease in internal pressure for judging that the internal pressure is decrease in case an average value of a specified number of the differences does not fall within a range of a preliminarily set threshold.
In accordance with the present invention, there is also provided a method for detecting decrease in air-pressure for use in a two-wheeled vehicle, including the steps of: detecting wheel speeds of a front and a rear wheel of a two-wheeled vehicle; obtaining accelerations of a vehicle body of the two-wheeled vehicle; calculating slip rates when the acceleration of the vehicle body is in a specified range which is proximate to zero; obtaining average values of the slip rates and average vehicle body speeds in case the accelerations of the vehicle body have continued to be in the specified range which is proximate to zero for a specified period of time; obtaining differences between the average values of the slip rates and a reference value which is based on an average vehicle body speed as preliminarily set when an internal pressure is normal; and judging that the internal pressure is decrease in case an average value of a specified number of the differences does not fall within a range of a preliminarily set threshold.
In accordance with the present invention, there is further provided a program for judging decompression for use in a two-wheeled vehicle so arranged that a computer is made to function as a wheel speed detecting means for detecting wheel speeds of a front and a rear wheel of a two-wheeled vehicle; an acceleration calculating means for obtaining accelerations of a vehicle body of the two-wheeled vehicle; a slip rate calculating means for calculating slip rates when the acceleration of the vehicle body is in a specified range which is proximate to zero; an average value calculating means for obtaining average values of the slip rates and average vehicle body speeds in case the accelerations of the vehicle body have continued to be in the specified range which is proximate to zero for a specified period of time; a difference calculating means for obtaining differences between the average values of the slip rates and a reference value which is based on an average vehicle body speed as preliminarily set when an internal pressure is normal; and a means for determining decrease in internal pressure for judging that the internal pressure is decrease in case an average value of a specified number of the differences does not fall within a range of a preliminarily set threshold.